1). Let's say path/to/newfilmroll contains some not yet imported pictures2). Pass this path twice on command line to darktable: darktable path/to/newfilmroll path/to/newfilmroll3). Only a couple of images will appear (just rectangles, no thumbs) and import will hang4). At least sometimes after that darktable doesn't cleanly exit, you may have to kill it

I have to point out that specifying directory as command line argument isn't the only way to trigger this bug, just the easiest to reproduce. There are import button, D'n'D, OS X open events... I really think this should be fixed (and not just by filtering command line arguments obviously).

I haven't checked if this is really an issue, just thinking loud: When importing an image we add a new entry to the db, and then query it to get the auto generated id. When the same image is imported twice I could imagine that the 2nd job inserts an entry but gets the id from the 1st job which could lead to problems. If it got the correct id it would just add a duplicate.